1. Field of the Invention
This invention relates to the use of phosphate esters of oxyalkylated thiols as corrosion inhibitors.
More particularly, the invention relates to the inhibition of corrosion in steel, iron and other ferrous metals which are exposed to the hostile environments of gas wells, especially deep gas wells, and, especially, in such wells characterized as "sweet systems", i.e., where the environment comprises a high concentration of carbon dioxide.
Although a wide variety of corrosion inhibitors are known, they are not effective in all systems. For example, a corrosion inhibitor which is effective at low temperature, atmospheric pressure and neutral or slightly acidic conditions would not necessarily be effective at high temperature, high pressure and highly acidic conditions. The mechanism of corrosion within a system is so unique that, despite theoretical considerations, selection of corrosion inhibitors is often more empirical then deducible.
As primary oil and gas fields become depleted, deeper wells are drilled to tap new sources of petroleum and gas. Increased depth, however, poses increasingly severe corrosion problems. The conditions of, for example, deep gas wells place great corrosive stress upon the tubing and other equipment employed in such wells due to the highly oxidizing atmospheres and extreme temperature and pressure conditions. Thus, when the drilling cost of a well is in excess of $5-6 million, approximately half of which is tubing, the importance of effective corrosion inhibition becomes evident. When conventional oil or gas well corrosion inhibitors are employed in deep wells, they are often found to have little or no effectiveness, since they tend to degrade or volatilize and either lose effectiveness as a corrosion inhibitor or polymerize and clog the tubing.
It has now been found that phosphate esters of oxyalkylated thiols, used alone or in conjunction with other materials, are effective corrosion inhibitors for ferrous metals used in gas and oil wells, particularly in deep gas wells.
The corrosion inhibitors of the present invention are particularly effective in systems containing a high concentration carbon dioxide.
2. Prior Art
U.S. Pat. No. 3,004,056 discloses the preparation of phosphate esters of certain oxyalkylated thiols and discloses their utility as surface active agents.